I've noticed that all of my ad blocks today on all sites are generating a page not found message instead of the ads. I logged into adsense and it says I've had a whopping 40 ad impressions today. That's rediculously low. I normally have a couple thousand by this time of the day. I clicked on site diagnostics and have no sites blocked, so I dont get it. Any idea as to what could be causing this? Should I notify google, or just assume that they are working on the issue?
You messed up with the new Website Filter? It allows you to show ads only on specified websites. Maybe you messed it up.
He wouldn't get the "page not found" error if that was the case. "Allowed Sites" feature doesn't stop ads from being displayed.
I've only ever seen that once on my site. A quick refresh solved the problem. E-mail google is the best option.